A honeycomb structure has been used in a filter for capturing particulate in exhaust gas of an internal combustion engine or a boiler, particularly used in a filter for capturing diesel particulate (it is hereinafter referred to as DPF) or a substrate for purifying exhaust gas, or the like.
The honeycomb structure for use in this purpose, in general, includes a large number of cells 3 partitioned by cell walls 2 and extending through an X-axis direction as shown in FIGS. 18(a) and 18(b). Furthermore, the structure for the DPF usually includes a structure in which the cells 3 disposed adjacent to each other are alternately plugged at ends on opposite sides so that end surfaces form checkered patterns. In such a honeycomb structure, a fluid to be treated flows in the cell 3 not plugged at inflow end face 42, that is, plugged at outflow end face 44, passes through the porous cell walls 2, and is discharged via the adjacent cells 3, that is, the cell 3 plugged at the inflow end face 42 and not plugged at outflow end face 44. In this case, the cell walls 2 act as a filter. For example, soot discharged from a diesel engine is trapped by the cell walls and deposited on the cell walls. In a honeycomb structure used in such a way, the sharp temperature change of exhaust gas and the local heating of the structure make non-uniform the temperature distribution inside the structure and there have been problems such as crack generation in honeycomb structure and the like. When the honeycomb structure is used particularly as a DPF, it is necessary to burn the fine carbon particles deposited on the filter to remove the particles and regenerate the filter and, in that case, high temperatures are inevitably generated locally in the filter; as a result, a big thermal stress and cracks have tended to generate.
To solve the problem, a method of bonding a plurality of divided segments of the honeycomb structure by a bond material has been proposed. For example, in U.S. Pat. No. 4,335,783, a method for manufacturing a honeycomb structure is disclosed in which a large number of honeycomb members are bonded by discontinuous bond materials. Also in JP-B-61-51240 is proposed a thermal-shock resistant rotary regenerating thermal exchanging method which comprises forming, by extrusion, matrix segments of honeycomb structure made of a ceramic material, firing them, making smooth, by processing, the outer peripheral portions of the fired segments, coating the to-be-bonded areas of the resulting segments with a ceramic adhesive having, when fired, substantially the same chemical composition as the matrix segments and showing a difference in thermal expansion coefficient, of 0.1% or less at 800° C., and firing the coated segments. In SAE document 860008 of 1986, a ceramic honeycomb structure is disclosed in which the honeycomb segment of cordierite is similarly bonded with cordierite cement. Further in JP-A-8-28246 is disclosed a ceramic honeycomb structure obtained by bonding honeycomb ceramic members with an elastic sealant made of at least a three-dimensionally intertwined inorganic fiber, an inorganic binder, an organic binder and inorganic particles.
A method in which a plurality of segments divided in this manner are integrated to suppress a local temperature rise is an effective method. However, this requires a step of producing many segments and thereafter integrating these segments in order to manufacture one honeycomb structure, and this is not economically favorable especially in a case where the structure needs to be divided into a large number of segments.
The present invention has been developed in consideration of the situations, and an object thereof is to provide a honeycomb structure which is not segmented or is integrally constituted of a smaller number of segments to suppress a local temperature rise and to reduce damages by a thermal stress at the time of use, and a method of manufacturing the honeycomb structure.